Regarding paper cups which are used after being filled with drinks, such as juice, and for which an upper opening portion is sealed with a lid member, paper cups formed with a joining portion provided to a barrel portion having a blank have generally been used. This blank is formed by punching a laminated material in a predetermined shape. In this laminated material, thermoplastic resin layers, such as polyethylene, are provided on both surfaces of the paper which is the base.
Additionally, when a barrier property against gas, such as oxygen or steam, is required, paper containers, such as a paper cup which is formed using a laminated material with a configuration including a layer having an excellent barrier property, have often been used. As this laminated material, for example a polyethylene film, paper, a polyethylene film, an aluminum foil, a polyethylene terephthalate film, and a polyethylene film, or a polyethylene film, paper, a polyethylene film, a plastic film having a metal oxide vapor-deposited layer, and a polyethylene film are used from the front side.
As a method of securing the barrier property of the joining portion of the paper cup, for example, there is known a method of performing end surface processing (edge protection) which protects end surfaces of both lateral ends of a joining portion of a barrel member which constitutes the barrel portion of the paper cup. This method is a method referred to as skive hemming as shown in FIGS. 2A to 2C.
In this method, a barrel member 100 made of a laminated sheet in which thermoplastic resin 102 is laminated on a paper base 101 is used (refer to FIG. 2A). An outermost layer end edge of the barrel member 100 is skived (cut) by approximately half of the thickness of the barrel member 100 by a cutting milling method or a cutting bell knife method (refer to FIG. 2B). Next, the barrel member 100 of the remaining skived (cut) half is hemmed such that the cut surface is placed inside (folded back), and a paper end surface is protected by the thermoplastic resin (refer to FIG. 2C).
As above, in order to perform skive-hemming process of the paper end surface, it is necessary to perform the skive-hemming process of the paper end surface using a special working machine before the barrel member (blank), which is punched in advance, is formed into a paper cup. Additionally, in order to trim a skived end surface on a straight line, it is difficult to perform cup forming simultaneously when a cup forming machine performs the skive-hemming process. As such, the skive-hemming process involves complicated working processes. Moreover, complete removal of debris generated by skiving (cutting) the paper base 101 is difficult.
Since management of skive depth is difficult in the skive-hemming process, there is a case where a scrap from the skived portion is generated after the forming. As a result, there is a problem in that side sealing or the like is not stable. In addition, in order to use glue for fold-back bonding after skiving in the skive hemming, management of the amount, position, or the like of the glue is difficult.
As a method of producing a cup-like paper container having an excellent barrier property without performing the skive-hemming process, a method of using a blank in which end surfaces of a paper base are covered with a film is proposed (for example, refer to the below Patent Documents 1 to 5).
In the cup-like paper container having a barrier property which protects the end surfaces of this paper base, a thermoplastic resin layer is prepared so as to extend from the paper base, over the whole inner end edge of an attached barrel overlap portion. Thus, the film of the thermoplastic resin layer extending from the paper base in this way will be irregularly formed during cup forming. For this reason, the original purpose of covering the end surfaces of the paper base cannot be sufficiently achieved. Additionally, since the finish as a cup-like paper container is poor, there is a problem in that a defect is caused in the appearance.
Moreover, a method of punching a laminated sheet based on paper in which a thermoplastic resin layer is provided at least on the inner surface in a predetermined shape, and then closely overlapping a resin portion extending outwardly from one lateral end edge of a blank such that the resin portion becomes the inside of the other end edge, thereby forming an attached barrel overlap portion is proposed (refer to the below Patent Document 2). This resin portion is closely covered with the blank along the end surfaces of the base.
Moreover, in an opening portion of the cup-like paper container, a flange portion is formed by winding an upper end edge of the barrel member one round or more.
By providing the flange portion at the opening portion of the cup-like paper container in this way, deformation of the paper container can be suppressed even when a force is applied thereto from the outside. Thus, it is possible to provide a paper container which is suitable for use as the mouthpiece of a drink container.
Moreover, since sealing can be performed by overlapping the top surface of the flange portion with a lid member, the cup-like paper container is suitable as a cup-like paper container for an application which requires sealing.
Additionally, in order to more easily perform sealing using the lid member, a flange portion prepared by winding an upper end edge of the barrel member is pressed from an up-and-down direction, and is brought into a flat state.
Ultrasonic means other than ordinary heating and pressing means can be used as the means for bringing the flange portion into the flat state.
As such, when the upper end edge of the barrel member is wound in the opening portion to form the flange portion, a stepped portion caused by the thickness of the paper which is the base is generated in the flange portion. Therefore, when the lid member is overlapped with the top surface of the flange portion, and is heated and sealed, sealing cannot be reliably performed due to the stepped portion. Particularly, when the flange portion is in a flat state, the influence caused by the thickness of the base is great.
Additionally, in order to fill the stepped portion of the top surface of the flange portion to reliably perform sealing, it is necessary to provide a filling member made of a separate resin or the like to eliminate the stepped portion, and partially perform sealing of the position of the stepped portion.
As such, when the lid member is overlapped with the top surface of the flange portion and sealed, a gap may be generated in the sealed portion of the lid member due to the level difference of the flange portion if the upper end edge is wound while the flange portion of the upper portion of the attached barrel overlap portion overlaps the paper base of the attached barrel overlap portion. Additionally, there are problems such as the finish as a cup-like container being poor, and a defect is caused in the appearance.
In order to solve this problem, in a cup-like paper container in which a tubular barrel member and a bottom member below this barrel member are integrated, a configuration in which the lateral end edge located inside the overlap portion of the blank has a resin portion extending from the lateral end edge of the base, and a cutout portion is provided in an upper portion of the lateral end edge which is not provided with the resin portion is suggested in the below Patent Document 5. This blank is made up of, for example, a laminated sheet based on paper which has a thermoplastic resin layer provided at least on the inner surface thereof. This tubular barrel member is formed with an attached barrel overlap portion obtained by overlapping one lateral end edge of the blank with the other lateral end edge, and a flange portion obtained by winding an upper end edge one round or more.
In this method, by providing a cutout portion in an upper portion of the lateral end edge of the barrel member, the barrel member is not wound while being overlapped in the flange portion of the upper portion of the attached barrel overlap portion. Therefore, a flange portion with a small level difference is formed, so that a gap of a sealed portion can be made small when sealed by the lid member.
However, the amount of resin required for bonding the lid member may be insufficient merely by providing the cutout portion in the upper portion of the lateral end edge of the barrel member which does not provide the resin portion. Moreover, the problem that the sealing using resin of the end surface of the barrel member in the upper flange portion of the attached barrel overlap portion becomes easily imperfect is left unsolved.
Moreover, a paper container in which a laminated sheet based on paper in which a thermoplastic resin layer is provided on the inner surface is punched in a predetermined shape, and then, a fold-back resin portion of the blank is closely overlapped with the base such that the resin portion becomes the inside of the other end edge, thereby forming an attached barrel overlap portion is proposed (refer to the below Patent Document 3). This fold-back resin portion is formed as the resin portion which extends outwardly from one lateral end edge and is folded back to the outer surface side.
This paper container is protected as the inner-surface-side base end surface in the attached barrel overlap portion is covered with the thermoplastic resin layer. Additionally, in the case of the cup-like container, the upper end edge of the barrel member is wound in the opening portion to form the flange portion. Therefore, a stepped portion caused by the thickness of the paper which is a base is generated in the flange portion. For this reason, when the lid member is overlapped with the top surface of the flange portion, and is heated and sealed, sealing cannot be reliably performed due to the stepped portion. The below Patent Document 3 suggests a solution to confront this problem.
However, a problem that the barrier property of the end surface of the lower end edge of the barrel member in a container bottom surface portion of the cup-like container is insufficient is left unsolved in terms of the protection of the end surface of the paper base. That is, while the end surface of the peripheral edge portion of the bottom member of the cup is pinched by the fold-back of the lower end of the barrel member, the lower end of the barrel member is fixed in the state of being folded back to the inside of the container, and the end surface is exposed to the air. Therefore, the cup is weak in terms of penetration of water through the paper end surface.